1. Field of the Invention
This invention relates in general to surface cleaning devices and in particular to a self-propelled surface cleaning apparatus that is self-guided so that it automatically traverses the area to be cleaned without any operator intervention, draws electrical power from a conventional electrical power socket via a flexible electrical power cable, and is convertible so that it can also be operated manually in the conventional manner.
2. Description of Related Art
Various surface cleaning devices have been developed and are in use for household and commercial applications. There is a need to automate operation of these devices to reduce the burden on the operator and also in cases where surfaces that have to be cleaned contain materials that are hazardous. Several embodiments of self-propelled automatic cleaning devices have been disclosed in the patent literature. A typical automatic cleaning apparatus comprises suction nozzles and/or brushes for cleaning the surface traversed by the cleaning apparatus, a drive system for propelling the cleaning apparatus over the area to be cleaned, a controller to direct the motion of the cleaning apparatus over the area to be cleaned, and associated sensors that detect the presence of obstacles, the condition of the surface to be cleaned, and the distance traversed by the cleaning apparatus. However, these embodiments have not been widely commercialized, because of several limitations that make them impractical and expensive to implement.
U.S. Pat. No. 3,789,939 issued to Geislinger, U.S. Pat. No. 4,700,427 issued to Knepper and U.S. Pat. No. 5,341,540 issued to Soupert et al disclose methods for self-guided movement of a cleaning apparatus in which the area to be cleaned is first manually traversed with the cleaning apparatus, and the path of motion is stored in the memory of the cleaning apparatus. During subsequent operation the cleaning apparatus uses the path stored in memory to traverse the area to be cleaned. This approach is not feasible for cleaning of areas that are in use since any rearrangement of the obstacles within the area to be cleaned, or a change in the starting position of the cleaning apparatus requires re-programming. Re-programming is tedious and detracts from the self-guiding feature of the cleaning apparatus.
Radio control methods for controlling the motion of the cleaning apparatus described in U.S. Pat. No. 4,369,543 issued to Chen et al and U.S. Pat. No. 4,513,469 issued to Godfrey et al are not truly self-guided methods since they require an operator to guide the motion of the cleaning apparatus albeit remotely. Another approach for self-guided movement uses guides as proposed in U.S. Pat. No. 5,095,577 issued to Jonas et at. For this method to be viable guides have to be installed in the area to be cleaned. Installation of guides is inconvenient for normal household and commercial applications. Also it may be necessary to clean a multitude of rooms, all of which may not be equipped with guides. Betker et al in U.S. Pat. No. 5,279,672 have proposed the use of coded reflective targets to provide information to the cleaning apparatus for positioning it along desired cleaning paths. While this mitigates the inconvenience and expense associated with the installation of guides, coded reflective targets have to be installed instead. In U.S. Pat. No. 5,293,955 to Lee guides are installed on the body of the cleaning apparatus. Similarly in U.S. Pat. No. 5,309,592 to Hiratsuka a sliding contact force sensor is used to maintain a safe distance from obstacles. Both these approaches do not work well with odd shaped obstacles that might be encountered during the cleaning operation.
U.S. Pat. No. 5,109,566 issued to Kobayashi et al proposes a method for self-guided motion of the cleaning apparatus that mitigates most of the limitations discussed earlier. The area to be cleaned is divided into a series of blocks, and an algorithm is used to automatically traverse the blocks. The algorithms used to traverse the room described in U.S. Pat. No. 5,109,566 have been further refined in U.S. Pat. No. 5,284,522 also issued to Kobayashi et al so that an arbitrarily shaped room with a random arrangement of obstacles within it can be automatically traversed by the cleaning apparatus. However, at the end of the cleaning operation, or in the case of obstacles that are U-shaped the cleaning apparatus must move from one position to the next that are physically disjoint. An automated procedure for accomplishing this motion has not been described, and thus presumably the cleaning apparatus relies on the aid of an operator to move the cleaning apparatus to its next position. Besides this shortcoming in the self-guiding procedure, the cleaning apparatus described is still impractical for normal home and commercial use due to other limitations of the prior art that have not been rectified. The electrical power source for the self-guided cleaning apparatus is an on-board battery and charger system. U.S. Pat. No. 4,173,809 to Ku also proposes an on-board battery for powering an automatic vacuum cleaner. Typical electrical power consumption of the electric motors that propel the cleaning apparatus and power the cleaning apparatus suction fan range from 1 kW-2 kW. Batteries that can supply these high electrical power levels are bulky, expensive, and require frequent charging. Charging is usually slow and typically requires 1-3 hours. This increases the time required for the apparatus to clean a large sized room since frequent charging is necessary. Thus using an on-board battery as the primary electrical power source is impractical for cleaning apparatus.
The self-guided cleaning apparatus described in U.S. Pat. No. 5,284,522 to Kobayashi et al also uses an elaborate combination of sensors for detecting obstacles (e.g. ultrasonic and touch sensitive proximity sensors), sensing distance traveled (e.g. rotary encoders), orientation of the cleaning apparatus (e.g. gyroscopes), and sensing the condition of the surface being cleaned. These sensors contribute significantly to the cost and complexity of the apparatus. Ultrasonic and touch sensitive sensors are not effective in detecting odd shaped obstacles. Often, dust particles and debris accumulate near the edges of obstacles, and it is necessary for the cleaning apparatus to contact the obstacle for effective cleaning. Ultrasonic sensors are not suited for detecting contact with odd shaped obstacles. Also, many of these sensors are critical for the self-guided operation since the cleaning apparatus has to return accurately to its home position for charging of its on-board battery.
Further, the self-guided cleaning apparatus requires steering mechanisms to enable movement of the cleaning apparatus in two mutually orthogonal directions. Steering mechanisms are complex, and require special sensors to detect the orientation of the apparatus. Detecting the position of the apparatus relative to the starting position is complicated and error-prone without the aid of a gyroscope. Steering is impossible if the turning radius of the cleaning apparatus is larger than the area being cleaned. This condition may arise while cleaning narrow confined spaces. A sharp ninety degree turn in moving direction, which is the basis of the algorithms disclosed, is not possible unless the turning radius of the cleaning apparatus is zero. A zero turning radius cannot be achieved with conventional steering mechanisms.
Thus while U.S. Pat. Nos. 5,109,566 and 5,284,522 teach methods that are substantial improvements over the prior art, further refinements are necessary to make a self-guided cleaning apparatus truly practical for normal home and commercial applications. The object of the present invention is to obviate the need for on-board battery power sources, elaborate steering mechanisms, and expensive sensors while providing a truly self-guided cleaning apparatus. The principal elements of this invention are the subject matter of US Document Disclosure No. 347,798 and are presented in this application.